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some wiring and plug help.

The shop where I work is moving. As part of the move we are looking to change all of our welders to the same plugs and input voltage. We have 1 - 251, 2 - 252's, 2 - syncrowave 200's, 1 - synchrowave 250, and 2 - 350p's.

I would like them all to be running 480v single phase. My question is what plug should I use that would be durable, appropriate for the amp draw, and relatively inexpensive (as we have to purchase a few of them).

Plugs and Wires

You have to check all your machines to make sure they are 480 compatible to connect to that voltage, if not you can blow them all up.

What I did with my dynasty 200 is wire the plug so it has common "hot" placements and then I can build pigtails to match the "hots" accordingly, but that welder is designed to change voltage and phase by itself.

If you want them all to have a 480 plug, then you have to make sure that you wire all your outlets the same. I mean, red, white, and blacks all need to be in the same spots. Then wire the plug on the machine to only have the white and black (W & B are the hots for a standard 220 plug) wired to the plug. So your plug will have 4 prongs to it, but only 2 will be hot, 1 will be ground, 1 will be a dud. AGAIN!!! make sure everything is wired the same, outlets and plugs.

Wires

If all your machines are 480 compatible, then you don't have to run down wires. Since a hot is a hot, and a ground is a ground in this case (it does matter for 3 phase though). Hots, don't have to be in the same order, they just have to be wired right at the panel. But if you do want to use the style of 220 pigtails off a 480 line in the future like if you get a MM180 or such, then you want to check now to make sure all wires are wired the same. That way when you move the 220 welder to a different plug, you don't have to worry about if your wired up right.

We will be doing the work ourselves due to time and work constraints. We want to have a minimum of down time. We are consolidating from our current sprawling cobbled together work space into our half used warehouse. While the guys are working, we will be running wire, argon lines, building racks and tables. When everything is ready for the move, we will call in the equipment movers to move the press brake, shear, and CNC tables over the weekend. While they are working we will move the air compressors, argon tanks and welders to their new home. The guys will be in on Monday and we will spend the rest of the week after hours buttoning up moving inventory, computers, and offices.

In our building there are 3 options.
1.do it yourself.
2.pay the maintenance guys to do it on their obviously precious and expensive time.
3.have an approved (read union) contractor do it. around us (rural pa) union guys are few and far between and they mostly work in Pittsburgh. getting them to travel out here is a pain and they don't want to work around the guys welding all day and they sure don't want to work after hours!

While I might find some help for some areas I was weak on I can relate to doing your own move. Nice to learn correct way, easy to make changes as needed. As for the technical side, may be deep but in general if you are doubling the voltage a supply wire the same as the cord is fine.
But,,,, personally unless there was a big technical reason to do so I would want to run at 240. There are some efficiency reasons to use hi voltage but they vary as to return. Are these running arc on 8 hrs a day, long electric runs? You already have this voltage available?

Connectors

By going to 480 volts you are probably lowering the price of the connector, by lowering the current. 100 amp connectors cost hundreds of dollars. But the popular NEMA 6-50 plug is only rated to 250 volts. Might be time to visit the local electrical supply store and see what they suggest. You need a 480V 50 amp connector, and that is not real common. Obviously you would be better off with a more or less standard connector instead of an orphan.

You might look at the Leviton CS816-4C, it is rated 50 amps and 480 volts. Or Hubble CS8465C or Hubbell CS8169. There is a connector used for big generators, I forget the CS number.

You should double check that all machines will run on single phase 480, and the current draw, but I think that 50 amps will work for 480. Welders have some exceptions in the National electrical code anyway, so peak current can exceed the rating, since welders are intermittent use items, usually limited by duty cycle.

Nope, I am not an electrician, but I do get involved with large generators.